The present invention relates to a method for the preparation of a silicon carbide-carbon fiber composite material or, more particularly, to a method for the preparation of a silicon carbide-based ceramic material reinforced with carbon fibers without causing a decrease in the mechanical strength, which method is applicable to a ceramic body of any complicated forms.
It is a noteworthy fact in recent years that the application fields of silicon carbide-based ceramic materials are rapidly expanding as a material of structural members working at extremely high temperatures, as a corrosion-resistant material and as an abrasion-resistant material in respect of the excellent high-temperature stability, corrosion resistance and abrasion resistance thereof.
On the other hand, intensive investigations are recently under way to develop a composite ceramic material reinforced with a fibrous reinforcing material with an object to improve the toughness of ceramic materials. For example, silicon carbide-based composite ceramic materials reinforced with a fibrous reinforcing material are prepared usually by blending a powder of silicon carbide and reinforcing fibers and subjecting the blend to sintering in a hot press or by the method of chemical vapor infiltration. The hot-press sintering method, however, is disadvantageous because full sintering can be achieved only by the admixture of the blend with a substantial amount of a sintering aid or by undertaking sintering at a high temperature of 1700.degree. C. or even higher unavoidably resulting in a decrease in the mechanical strength of the sintered body in addition to the limitation that the method is hardly applicable to the preparation of a sintered body having a complicated form. The chemical vapor infiltration method, on the other hand, has problems that the time taken for the infiltration is usually so long that the productivity of the process is low and the reactant gases used for the method, such as methyltrichlorosilane, sometimes have toxicity although the temperature for the process is not so high as in the hot-press sintering method and the method is applicable to the preparation of a ceramic body having a relatively complicated form.
As a method for the preparation of silicon carbide-based ceramic materials, a proposal is made for a method involving in situ formation of silicon carbide by a chemical reaction. For example, a green compact body composed of particles of silicon carbide and particles of graphite is infiltrated with a melt of elementary silicon so that silicon carbide is formed in situ by the reaction of the graphite particles and the molten silicon. A problem in this method is that the molten silicon must be at a high temperature of 1600.degree. C. or higher in order to effect smooth and complete infiltration of the green compact body with the molten silicon despite the melting point of elementary silicon of about 1410.degree. C.
Further, a method is proposed in American Ceramic Society Bulletin, volume 65, No. 2, pages 326 to 335 (1986) for the preparation of a fiber-reinforced silicon carbide-based composite ceramic material by utilizing the reaction between carbon of a carbon fiber-reinforced carbon composite and silicon, according to which a composite body of carbon fibers in a carbon matrix is infiltrated with molten silicon to effect the reaction between the carbon matrix and the molten silicon so that a silicon carbide-based composite ceramic body reinforced with carbon fibers can be obtained. This method has problems that the reaction cannot proceed uniformly throughout the compact body and the reaction of the molten silicon may take place not only with the carbon matrix but also with the carbon fibers thus to decrease the reinforcing effect of the carbon fibers. Therefore, it is generally understood that the infiltration method with molten silicon is not suitable for the preparation of a silicon-carbide-based composite ceramic body reinforced with carbon fibers.
Alternatively, a method is proposed in Journal of Japan Ceramic Society, volume 94, No. 5, pages 512 to 516 (1986) for the preparation of a sintered body of silicon carbide by subjecting a blend of powders of silicon and carbon to the process of pressurized self-combustion sintering. This method has almost no prospect of industrialization because sintering therein must be performed at an extremely high temperature of 2000.degree. C. or higher and under a high pressure of at least 3 GPa if not to mention the inapplicability of the method to the preparation of a carbon fiber-reinforced silicon carbide body.